Method and device for transmitting and receiving primary synchronization signal in wireless access system supporting narrowband internet of things

ABSTRACT

The present invention provides a method and devices for transmitting and receiving a synchronization signal and a method for generating a synchronization signal in a wireless access system supporting narrowband Internet of Things (NB-IoT). A method for transmitting a primary synchronization signal (PSS) by a base station in a wireless access system supporting narrowband Internet of Things (NB-IoT), according to an embodiment of the present invention, can comprise the steps of: repeatedly generating first sequences n times so as to generate primary synchronization signals; multiplying n first sequences by second sequences and thus generating n primary synchronization signals; and transmitting n primary synchronization signals by means of n OFDM symbols, respectively. The size of a bandwidth used in the wireless access system supporting NB-IoT is the size of one physical resource block (PRB), and one PRB can comprise twelve subcarriers in a frequency domain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 37 U.S.C. 371 ofInternational Application No. PCT/KR2016/011043, filed on Oct. 4, 2016,which claims the benefit of U.S. Provisional Application Nos.62/236,849, filed on Oct. 2, 2015, 62/264,875, filed on Dec. 9, 2015,62/266,004, filed on Dec. 11, 2015, and 62/311,972, filed on Mar. 23,2016.

TECHNICAL FIELD

The present disclosure relates to a wireless access system supportingnarrowband Internet of things (NB-IoT), and more particularly, to amethod for generating a synchronization signal, a method fortransmitting and receiving a synchronization signal, and apparatuses.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, and a single carrier frequency division multipleaccess (SC-FDMA) system.

DISCLOSURE Technical Problem

An aspect of the present disclosure is to provide a method fortransmitting and receiving data and/or control information for anarrowband Internet of things (NB-IoT) user equipment (UE).

Another aspect of the present disclosure is to provide a method forgenerating a primary synchronization signal and a secondarysynchronization signal in an NB-IoT system.

Another aspect of the present disclosure is to provide a method fortransmitting and receiving a primary synchronization signal and asecondary synchronization signal in an NB-IoT system.

Another aspect of the present disclosure is to provide apparatusessupporting the above methods.

Additional advantages, objects, and features of the present disclosurewill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of thepresent disclosure. The objectives and other advantages of the presentdisclosure may be realized and attained by the structure particularlypointed out in the written description and claims hereof as well as theappended drawings.

Technical Solution

The present disclosure provides a method for generating asynchronization signal, a method for transmitting and receiving asynchronization signal, and apparatuses in a wireless access systemsupporting narrowband Internet of things (NB-IoT).

According to an aspect of the present disclosure, a method oftransmitting a primary synchronization signal (PSS) in a wireless accesssystem supporting narrowband Internet of things (NB-IoT) includesrepeatedly generating a first sequence N times in order to generate thePSS, multiplying the N first sequences by a second sequence to generateN PSSs, and transmitting the N PSSs through N orthogonal frequencydivision multiplexing (OFDM) symbols. At this time, a bandwidth used inthe wireless access system supporting NB-IoT is one PRB, and the PRBincludes 12 subcarriers in the frequency domain.

According to another aspect of the present disclosure, a base stationfor transmitting a primary synchronization signal (PSS) in a wirelessaccess system supporting narrowband Internet of things (NB-IoT) includesa transmitter and a processor. The processor is configured to repeatedlygenerate a first sequence N times in order to generate the PSS, tomultiply the N first sequences by a second sequence to generate N PSSs,and to control the transmitter to transmit the N PSSs through Northogonal frequency division multiplexing (OFDM) symbols. At this time,a bandwidth used in the wireless access system supporting NB-IoT is onePRB, and the PRB includes 12 subcarriers in the frequency domain.

In the aspects, the base station may transmit the N OFDM symbols with“0” filled in resource elements, to which the PSSs are not allocated.

The N OFDM symbols may be included in one subframe. The N OFDM symbolsmay include OFDM symbols except for a control region in the subframe.

The first sequence may be generated from a Zadoff-Chu (ZC) sequence.

The second sequence may be determined in consideration of the number ofOFDM symbols in which the PSS signals are transmitted.

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

Advantageous Effects

Accordingly, the present disclosure provides the following effectsand/or advantages.

First, data and/or control information for a narrowband Internet ofthings (NB-IoT) user equipment (UE) can be efficiently transmitted andreceived.

Secondly, as methods for generating a primary synchronization signal(PSS) and a secondary synchronization signal (SSS) used in an NB-IoTsystem are defined, an NB-IoT UE can efficiently acquire time andfrequency synchronization even in an NB-IoT system.

Thirdly, as methods for generating an SSS used in an NB-IoT system areprovided, a UE can acquire a physical cell identifier (ID) of a servingcell, subframe position information, and so on in the NB-IoT system.

Fourthly, as a method for transmitting and receiving a PSS and an SSS ina narrowband applied to an NB-IoT system is provided, a UE can activelysynchronize with a base station (BS).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithin the scope of the appended claims and the embodiments described inthe descriptions hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiments of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a view illustrating physical channels and a signaltransmission method using the physical channels;

FIG. 2 is a view illustrating exemplary radio frame structures;

FIG. 3 is a view illustrating an exemplary resource grid for theduration of a downlink slot;

FIG. 4 is a view illustrating an exemplary structure of an uplinksubframe;

FIG. 5 is a view illustrating an exemplary structure of a downlinksubframe;

FIG. 6 is a view illustrating an example of component carriers (CCs) andcarrier aggregation (CA) in a Long Term Evolution-Advanced (LTE-A)system;

FIG. 7 is a view illustrating a subframe structure based oncross-carrier scheduling in the LTE-A system;

FIG. 8 is a conceptual view of a coordinated multi-point (CoMP) systemoperating in a CA environment;

FIG. 9 is a view illustrating an exemplary subframe to whichcell-specific reference signals (CRSs) are allocated, which may be usedin embodiments of the present disclosure;

FIG. 10 is a view illustrating exemplary subframes to which channelstate information reference signals (CSI-RSs) are allocated according tonumbers of antenna ports, which may be used in embodiments of thepresent disclosure;

FIG. 11 is a view illustrating exemplary multiplexing of a legacyphysical downlink control channel (PDCCH), a physical downlink sharedchannel (PDSCH), and an enhanced PDCCH (EPDCCH) in an LTE/LTE-A system;

FIG. 12 is a view illustrating an exemplary frame structure showing aposition for transmitting a synchronization signal;

FIG. 13 is a view illustrating a method for generating a secondarysynchronization signal (SSS);

FIG. 14 is a view illustrating a method for transmitting a primarysynchronization signal (PSS) in a specific subframe in a narrowbandInternet of things (NB-IoT) system;

FIG. 15 is a view illustrating a method for generating a PSS in theNB-IoT system;

FIG. 16 is a view illustrating correlation characteristics according tocover code patterns required for generating a PSS;

FIG. 17 is a view illustrating a method for transmitting an SSS in aspecific subframe in the NB-IoT system;

FIG. 18 is a view illustrating a method for generating an SSS in aspecific subframe in the NB-IoT system;

FIG. 19 is a view illustrating another method for transmitting an SSS ina specific subframe in the NB-IoT system;

FIG. 20 is a view illustrating a method for generating an SSS withoutconsidering a scrambling sequence; and

FIG. 21 is a block diagram of apparatuses for implementing the methodsdescribed with reference to FIGS. 1 to 20.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present disclosure as described below in detailrelate to a wireless access system supporting narrowband Internet ofthings (NB-IoT), and more particularly, to a method for generating asynchronization signal, and a method and apparatuses for transmittingand receiving a synchronization signal.

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentdisclosure (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a basestation (BS) and a user equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a mobile station (MS), a subscriber station (SS), amobile subscriber station (MSS), a mobile terminal, an advanced mobilestation (AMS), etc.

A transmission end is a fixed and/or mobile node that provides a dataservice or a voice service and a reception end is a fixed and/or mobilenode that receives a data service or a voice service. Therefore, a UEmay serve as a transmission end and a BS may serve as a reception end,on an uplink (UL). Likewise, the UE may serve as a reception end and theBS may serve as a transmission end, on a downLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

Hereinafter, 3GPP LTE/LTE-A systems are explained, which are examples ofwireless access systems.

The embodiments of the present disclosure can be applied to variouswireless access systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present disclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell identifier (ID) byreceiving a primary synchronization channel (P-SCH) and a secondarysynchronization channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aphysical broadcast channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a downlink reference signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a physical random access channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a physical uplink shared channel (PUSCH)and/or a physical uplink control channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled uplink control information (UCI). The UCI includes a hybridautomatic repeat and request acknowledgement/negative acknowledgement(HARQ-ACK/NACK), a scheduling request (SR), a channel quality indicator(CQI), a precoding matrix index (PMI), a rank indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2(a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full frequency division duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (Tf=307200·Ts) long, including equal-sized 20slots indexed from 0 to 19. Each slot is 0.5 ms (Tslot=15360·Ts) long.One subframe includes two successive slots. An ith subframe includes2ith and (2i+1)th slots. That is, a radio frame includes 10 subframes. Atime required for transmitting one subframe is defined as a transmissiontime interval (TTI). Ts is a sampling time given as Ts=1/(15kHz×2048)=3.2552×10-8 (about 33 ns). One slot includes a plurality oforthogonal frequency division multiplexing (OFDM) symbols or SC-FDMAsymbols in the time domain by a plurality of resource blocks (RBs) inthe frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 isapplied to a time division duplex (TDD) system. One radio frame is 10 ms(Tf=307200·Ts) long, including two half-frames each having a length of 5ms (=153600·Ts) long. Each half-frame includes five subframes each being1 ms (=30720·Ts) long. An ith subframe includes 2ith and (2i+1)th slotseach having a length of 0.5 ms (Tslot=15360·Ts). Ts is a sampling timegiven as Ts=1/(15 kHz×2048)=3.2552×10-8 (about 33 ns).

A type-2 frame includes a special subframe having three fields, downlinkpilot time slot (DwPTS), guard period (GP), and uplink pilot time slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink UpPTS Extended cyclic prefix indownlink Normal Extended UpPTS Special subframe cyclic prefix cyclicprefix Normal cyclic Extended cyclic configuration DwPTS in uplink inuplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s) 2192 ·T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a resource element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, NDLdepends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a physical control formatindicator channel (PCFICH), a PDCCH, and a physical hybrid ARQ indicatorchannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called downlink control information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL transmission (Tx) power control commands for a UE group.

1.2 Physical Downlink Control Channel (PDCCH)

1.2.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a downlink shared channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran uplink shared channel (UL-SCH) (i.e. a UL grant), paging informationof a paging channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, voice over Internetprotocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive control channel elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel. ACCE includes a plurality of RE groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.2.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four quadrature phase shift keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by NREG. Then thenumber of CCEs available to the system is NCCE (=└N_(REG)/9┘) and theCCEs are indexed from 0 to NCCE−1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0.

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 PDCCH Number of Number of Number of format CCE (n) REG PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or modulation and coding scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format 0 Resource grants for PUSCHtransmissions (uplink) Format 1 Resource assignments for single codewordPDSCH transmission (transmission modes 1, 2 and 7) Format 1A Compactsignaling of resource assignments for single codeword PDSCH (all modes)Format 1B Compact resource assignments for PDSCH using rank-1 closedloop precoding (mode 6) Format 1C Very compact resource assignments forPDSCH (e.g., paging/broadcast system information) Format 1D Compactresource assignments for PDSCH using multi-user MIMO (mode 5) Format 2Resource assignments for PDSCH for closed loop MIMO operation (mode 4)Format 2A resource assignments for PDSCH for open loop MIMO operation(mode 3) Format 3/3A Power control commands for PUCCH and PUSCH with2-bit/1-bit power adjustment Format 4 Scheduling of PUSCH in one UL cellwith multi-antenna port transmission mode

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission oftransmission power control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher-layer signaling(e.g. radio resource control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically byhigher-layer signaling. For example, multi-antenna transmission schememay include transmit diversity, open-loop or closed-loop spatialmultiplexing, multi-user multiple input multiple output (MU-MIMO), orbeamforming. Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing thesignal to interference plus noise ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 10 transmission modes are availableto UEs:

(1) Transmission mode 1: Single antenna port (port 0);

(2) Transmission mode 2: Transmit diversity;

(3) Transmission mode 3: Open-loop spatial multiplexing when the numberof layer is larger than 1 or Transmit diversity when the rank is 1;

(4) Transmission mode 4: Closed-loop spatial multiplexing;

(5) Transmission mode 5: MU-MIMO;

(6) Transmission mode 6: Closed-loop rank-1 precoding;

(7) Transmission mode 7: Precoding supporting a single layertransmission, which is not based on a codebook (Rel-8);

(8) Transmission mode 8: Precoding supporting up to two layers, whichare not based on a codebook (Rel-9);

(9) Transmission mode 9: Precoding supporting up to eight layers, whichare not based on a codebook (Rel-10); and

(10) Transmission mode 10: Precoding supporting up to eight layers,which are not based on a codebook, used for CoMP (Rel-11).

1.2.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a cyclic redundancy check (CRC) to thecontrol information. The CRC is masked by a unique identifier (ID) (e.g.a radio network temporary identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a system information block(SIB), its CRC may be masked by a system information ID (e.g. a systeminformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a random access-RNTI (RA-RNTI).

Then, the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.2.4 Blind Decoding (BD)

A plurality of PDCCHs may be transmitted in a subframe. That is, thecontrol region of a subframe includes a plurality of CCEs, CCE 0 to CCENCCE,k−1. NCCE,k is the total number of CCEs in the control region of akth subframe. A UE monitors a plurality of PDCCHs in every subframe.This means that the UE attempts to decode each PDCCH according to amonitored PDCCH format.

The eNB does not provide the UE with information about the position of aPDCCH directed to the UE in an allocated control region of a subframe.Without knowledge of the position, CCE aggregation level, or DCI formatof its PDCCH, the UE searches for its PDCCH by monitoring a set of PDCCHcandidates in the subframe in order to receive a control channel fromthe eNB. This is called blind decoding. Blind decoding is the process ofdemasking a CRC part with a UE ID, checking a CRC error, and determiningwhether a corresponding PDCCH is a control channel directed to a UE bythe UE.

The UE monitors a PDCCH in every subframe to receive data transmitted tothe UE in an active mode. In a discontinuous reception (DRX) mode, theUE wakes up in a monitoring interval of every DRX cycle and monitors aPDCCH in a subframe corresponding to the monitoring interval. ThePDCCH-monitored subframe is called a non-DRX subframe.

To receive its PDCCH, the UE should blind-decode all CCEs of the controlregion of the non-DRX subframe. Without knowledge of a transmitted PDCCHformat, the UE should decode all PDCCHs with all possible CCEaggregation levels until the UE succeeds in blind-decoding a PDCCH inevery non-DRX subframe. Since the UE does not know the number of CCEsused for its PDCCH, the UE should attempt detection with all possibleCCE aggregation levels until the UE succeeds in blind decoding of aPDCCH.

In the LTE system, the concept of search space (SS) is defined for blinddecoding of a UE. An SS is a set of PDCCH candidates that a UE willmonitor. The SS may have a different size for each PDCCH format. Thereare two types of SSs, common search space (CSS) andUE-specific/dedicated search space (USS).

While all UEs may know the size of a CSS, a USS may be configured foreach individual UE. Accordingly, a UE should monitor both a CSS and aUSS to decode a PDCCH. As a consequence, the UE performs up to 44 blinddecodings in one subframe, except for blind decodings based on differentCRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).

In view of the constraints of an SS, the eNB may not secure CCEresources to transmit PDCCHs to all intended UEs in a given subframe.This situation occurs because the remaining resources except forallocated CCEs may not be included in an SS for a specific UE. Tominimize this obstacle that may continue in the next subframe, aUE-specific hopping sequence may apply to the starting point of a USS.

[Table 4] illustrates the sizes of CSSs and USSs.

TABLE 4 PDCCH Number of Number of Number of Format CCE (n) candidates inCSS candidates in USS 0 1 — 6 1 2 — 6 2 4 4 2 3 8 2 2

To mitigate the load of the UE caused by the number of blind decodingattempts, the UE does not search for all defined DCI formatssimultaneously. Specifically, the UE always searches for DCI Format 0and DCI Format 1A in a USS. Although DCI Format 0 and DCI Format 1A areof the same size, the UE may distinguish the DCI formats by a flag forformat 0/format 1a differentiation included in a PDCCH. Other DCIformats than DCI Format 0 and DCI Format 1A, such as DCI Format 1, DCIFormat 1B, and DCI Format 2 may be required for the UE.

The UE may search for DCI Format 1A and DCI Format 1C in a CSS. The UEmay also be configured to search for DCI Format 3 or 3A in the CSS.Although DCI Format 3 and DCI Format 3A have the same size as DCI Format0 and DCI Format 1A, the UE may distinguish the DCI formats by a CRCscrambled with an ID other than a UE-specific ID.

An SS S_(k) ^((L)) is a PDCCH candidate set with a CCE aggregation levelL∈{1, 2, 4, 8}. The CCEs of PDCCH candidate set m in the SS may bedetermined by the following equation.L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  [Equation 1]

Herein, M^((L)) is the number of PDCCH candidates with CCE aggregationlevel L to be monitored in the SS, m=0, . . . , M^((L))−1, i is theindex of a CCE in each PDCCH candidate, and i=0, . . . , L−1.k=└n_(s)/2┘ where n_(s) is the index of a slot in a radio frame.

As described before, the UE monitors both the USS and the CSS to decodea PDCCH. The CSS supports PDCCHs with CCE aggregation levels {4, 8} andthe USS supports PDCCHs with CCE aggregation levels {1, 2, 4, 8}. [Table5] illustrates PDCCH candidates monitored by a UE.

TABLE 5 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1  6 6 specific 2 12 6 4  8 2 816 2 Common 4 16 4 8 16 2

Referring to [Equation 1], for two aggregation levels, L=4 and L=8,Y_(k) is set to 0 in the CSS, whereas Y_(k) is defined by [Equation 2]for aggregation level L in the USS.Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

Herein, Y⁻¹=n_(RNTI)≠0, n_(RNTI) indicating an RNTI value. A=39827 andD=65537.

1.3 Carrier Aggregation (CA) Environment

1.3.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses multi-carrier Modulation (MCM) in which asingle component carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of radio frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a primacy cell (PCell) and a secondary cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellld is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a primary CC (PCC) and a PCell may be usedin the same meaning and a secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

FIG. 6(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 6(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 6(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≤N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≤M≤N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by system information block type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

1.3.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher-layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a carrier indicator field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set may bedefined within the UE DL CC set. That is, the eNB transmits a PDCCH onlyin the PDCCH monitoring set to schedule a PDSCH or PUSCH for the UE.

FIG. 7 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present disclosure.

Referring to FIG. 7, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher-layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC ‘C’ that are not configured as PDCCHmonitoring DL CCs.

1.3.3 CA Environment-Based CoMP Operation

Hereinafter, a cooperation multi-point (CoMP) transmission operationapplicable to the embodiments of the present disclosure will bedescribed.

In the LTE-A system, CoMP transmission may be implemented using acarrier aggregation (CA) function in the LTE. FIG. 8 is a conceptualview illustrating a CoMP system operating based on a CA environment.

In FIG. 8, it is assumed that a carrier operated as a PCell and acarrier operated as an SCell may use the same frequency band on afrequency axis and are allocated to two eNBs geographically spaced apartfrom each other. At this time, a serving eNB of UE1 may be allocated tothe PCell, and a neighboring cell causing much interference may beallocated to the SCell. That is, the eNB of the PCell and the eNB of theSCell may perform various DL/UL CoMP operations such as jointtransmission (JT), CS/CB and dynamic cell selection for one UE.

FIG. 8 illustrates an example that cells managed by two eNBs areaggregated as PCell and SCell with respect to one UE (e.g., UE1).However, as another example, three or more cells may be aggregated. Forexample, some cells of three or more cells may be configured to performCoMP operation for one UE in the same frequency band, and the othercells may be configured to perform simple CA operation in differentfrequency bands. At this time, the PCell does not always need toparticipate in CoMP operation.

1.4 System Information Block (SIB)

SIBs are used for an eNB to transmit system information. That is, a UEmay acquire system information by receiving different SIBs from the eNB.The SIBs are transmitted on a DL-SCH at the logical layer, and on aPDSCH at the physical layer. It is determined whether there is an SIB,by a PDCCH signal masked with a System Information Radio NetworkTemporary Identifier (SI-RNTI).

Among the SIBs, SIB type 1 (SIB1) includes parameters required todetermine whether a corresponding cell is suitable for cell selection,and information about time-axis scheduling of other SIBs. SIB type 2(SIB2) includes common channel information and shared channelinformation. SIB3 to SIB8 include cell reselection-related information,inter-frequency information, intra-frequency information, and so on.SIB9 is used to indicate the name of a home eNode B (HeNB), and SIB10,SIB11, and SIB12 include an earthquake and tsunami warning service(ETWS) notification and a commercial mobile alert system (CMAS) alertmessage. SIB13 includes multimedia broadcast multicast service(MBMS)-related control information.

Herein, SIB1 includes cell access-related parameters and schedulinginformation about other SIBs. SIB1 is transmitted every 80 ms, and a UEshould be able to receive SIB1 in idle mode/connected mode. SIB1 istransmitted every 80 ms, and a UE should be able to receive SIB1 in idlemode/connected mode. Transmission of SIB1 starts in subframe #5 of aradio frame satisfying SFN mod 8=0 and proceeds in subframe #5 of aradio frame satisfying SFN mod 2=0. SIB1 is transmitted, including thefollowing information.

TABLE 6 SystemInformationBlockType1 ::= SEQUENCE { cellAccessRelatedInfoSEQUENCE { plmn-IdentityList PLMN-IdentityList, trackingAreaCodeTrackingAreaCode, cellIdentity CellIdentity, cellBarred ENUMERATED{barred, notBarred}, intraFreqReselection ENUMERATED {allowed,notAllowed} csg-Indication BOOLEAN, csg-Identity CSG-Identity OPTIONAL-- Need OR }, cellSelectionInfo SEQUENCE { q-RxLevMin Q-RxLevMin,q-RxLevMinOffset INTEGER (1..8) OPTIONAL -- Need OP }, p-Max P-MaxOPTIONAL, -- Need OP freqBandIndicator FreqBandIndicator,schedulingInfoList SchedulingInfoList, tdd-Config TDD-Config OPTIONAL,-- Cond TDD si-WindowLength ENUMERATED { ms1, ms2, ms5, ms10, ms15,ms20, ms40}, systemInfoValueTag INTEGER (0..31), nonCriticalExtensionSystemInformationBlockType1-v890-IEs OPTIONAL } SchedulingInfoList ::=SEQUENCE (SIZE (1..maxSI−Message)) OF SchedulingInfo SehedulingInfo ::=SEQUENCE { si-Periodicity ENUMERATED { rf8, rf16, rf32, rf64, rf128,rf256, rf512}, sib-MappingInfo SIB-MappingInfo } SIB-MappingInfo ::=SEQUENCE (SIZE (0..maxSIB−1)) OF SIB-Type SIB-Type ::= ENUMERATED {sibType3, sibType4, sibType5, sibType6, sibType7, sibType8, sibType9,sibType10, sibType11, sibType12-v920, sibType13-v920, sibType14-v1130,sibType15-v1130, sibType16-v1130, sibType17-v-12xy, spare1, ...}

For a description of the parameters included in SIB1, as listed in[Table 6], refer to sub-clauses 5.2.2.7 and 6.2.2 of 3GPP TS 36.331.

SI messages may be transmitted within a time area (i.e., an SI window)generated periodically by dynamic scheduling. Each SI message is relatedto a specific SI window, and the specific SI windows do not overlap withother SI messages. A common SI window length may be set for all SImessages.

Within an SI window, a corresponding SI message is transmitted aplurality of times in all subframes except for MBSFN subframes, and ULsubframes and subframes #5 of radio frames satisfying SFN mod 2=0 inTDD. A UE may acquire specific time-domain scheduling information fromSI messages.

RVs are determined for a PDSCH scheduled by a PDCCH masked with anSI-RNTI in DCI format 1C, according to the following [Equation 3].RV _(K)=ceiling(3/2*k)modulo 4  [Equation 3]

In [Equation 3], k is determined according to the type of an SI message.For example, k=(SFN/2) modulo 4 for an SIB1 message. Here, SFNrepresents a system frame number. For each piece of system information,k=i modulo 4 and i=0, 1, . . . , nsw−1 where i represents the number ofa subframe within an SI window n_(s) ^(w).

1.5 Method for Transmitting Paging Message

A paging message is used to deliver paging information, SI messageupdate information, a public warning system (PWS) message, or the like.A default paging cycle may be set for each cell and a dedicated pagingcycle may be set for each UE, for transmission of a paging message. Iftwo or more paging cycles are set for a UE, a minimum paging cyclebecomes the paging cycle of the UE.

Paging subframes available for transmission of a paging message may becalculated by [Equation 4].SFN mod T=(T/N)×(UE_ID mod N)  [Equation 4]

In embodiments of the present disclosure, i_s represents an indexindicating a predefined table that defines paging subframes, andi_s=floor(UE_ID/N) mod NS. In [Equation 4], T is the UE discontinuousreception (DRX) cycle of the UE and may be given as T=min(Tc,TUE) whereTc is a cell-specific default paging cycle which may be set to {32, 64,128, 256} radio frames, and TUE is a UE-specific paging cycle which maybe set to {32, 64, 128, 256} radio frames. N represents the number ofpaging frames within one paging cycle, and may be given as N=min(T, nB)where nB is the number of paging subframes per paging cycle {4T, 2T, T,T/2, T/4, T/8, T/16, T/32}. NS represents the number of paging subframesin a radio frame used for paging and it is configured that Ns=max(1,nB/T).

[Table 7] and [Table 8] below illustrate paging subframe patterns in FDDand TDD, respectively.

TABLE 7 PO when PO when PO when PO when Ns i_s = 0 i_s = 1 i_s = 2 i_s =3 1 9 N/A N/A N/A 2 4 9 N/A N/A 4 0 4 5 9

TABLE 8 PO when PO when PO when PO when Ns i_s = 0 i_s = 1 i_s = 2 i_s =3 1 0 N/A N/A N/A 2 0 5 N/A N/A 4 0 1 5 6

[Table 9] illustrates exemplary paging subframes determined according to[Equation 4] and paging-related parameters.

TABLE 9 Case UE_ID T_(c) T_(UE) T nB N N_(s) PF i_s PO A 147 256 256 25664 64 1 76 0 9 B 147 256 128 128 32 32 1 76 0 9 C 147 256 128 128 256128 2 19 1 4

1.6 Reference Signal (RS)

Now, a description will be given of RSs that may be used in embodimentsof the present disclosure.

FIG. 9 is a view illustrating an exemplary subframe in whichcell-specific reference signals (CRSs) are allocated, which may be usedin embodiments of the present disclosure.

FIG. 9 illustrates a CRS allocation structure, when a system supportsfour antennas. CRS is used for the purpose of decoding and channel statemeasurement in the 3GPP LTE/LTE-A system. Therefore, CRSs aretransmitted across a total DL bandwidth in every DL subframe in a cellsupporting PDSCH transmission, and through all antenna ports configuredfor an eNB.

Specifically, a CRS sequence is mapped to complex-valued modulationsymbols used as reference symbols for antenna port p in slot ns.

A UE may measure CSI using CRSs and decode a DL data signal received ona PDSCH in a subframe including CRSs, using the CRSs. That is, the eNBtransmits CRSs at predetermined positions in every RB, and the UEperforms channel estimation based on the CRSs and then detects thePDSCH. For example, the UE measures signals received in CRS REs. The UEmay detect a PDSCH signal in REs to which the PDSCH is mapped, based onthe ratio between per-CRS RE reception energy and per-PDSCH RE receptionenergy.

If a PDSCH signal is transmitted based on CRSs in this manner, the eNBshould transmit CRSs in all RBs, resulting in unnecessary RS overhead.To solve the problem, the 3GPP LTE-A system additionally definesUE-specific RS (hereinafter, referred to as UE-RS) and channel stateinformation reference signal (CSI-RS) as well as CRS. UE-RS is used fordemodulation, and CSI-RS is used for deriving CSI.

Since UE-RS and CRS are used for demodulation, they may be referred toas demodulation RS in terms of their usage. That is, UE-RS may beregarded as a kind of Demodulation Reference Signal (DM-RS). Further,since CSI-RS and CRS are used for channel measurement or channelestimation, they may be regarded as channel state measurement RS interms of their usage.

FIG. 10 is a view illustrating exemplary subframes in which CSI-RSs areallocated according to numbers of antenna ports, which may be used inembodiments of the present disclosure.

CSI-RS is a DL RS which has been introduced to the 3GPP LTE-A system,for the purpose of radio channel state measurement, not demodulation.The 3GPP LTE-A system defines a plurality of CSI-RS configurations forCSI-RS transmission. A CSI-RS sequence is mapped to complex-valuedmodulation symbols used as reference symbols for antenna port p insubframes for which CSI-RS transmission is configured.

FIG. 10(a) illustrates 20 CSI-RS configurations, CSI-RS configuration 0to CSI-RS configuration 19 available for CSI-RS transmission through 2CSI ports, among CSI-RS configuration, FIG. 10(b) illustrates 10 CSI-RSconfigurations, CSI-RS configuration 0 to CSI-RS configuration 9available for CSI-RS transmission through 4 CSI ports, among the CSI-RSconfigurations, and FIG. 10(c) illustrates 5 CSI-RS configurations,CSI-RS configuration 0 to CSI-RS configuration 4 available for CSI-RStransmission through 8 CSI ports, among the CSI-RS configurations.

Herein, a CSI-RS port refers to an antenna port configured for CSI-RStransmission. A different CSI-RS configuration is used according to thenumber of CSI-RS ports. Therefore, in spite of the same CSI-RSconfiguration number, the CSI-RS configuration is different for adifferent number of antenna ports configured for CSI-RS transmission.

Compared to CRSs configured to be transmitted in every subframe, CSI-RSsare configured to be transmitted in every predetermined transmissionperiod corresponding to a plurality of subframes. Accordingly, theCSI-RS configuration differs according to a subframe for which CSI-RSsare configured as well as the positions of REs occupied by CSI-RSs in anRB pair.

Despite the same CSI-RS configuration number, the CSI-RS configurationmay be considered to be different in a different subframe for CSI-RStransmission. For example, if a CSI-RS transmission period T_(CSI-RS) isdifferent or a starting subframe ΔCSI-RS in which CSI-RS transmission isconfigured in a radio frame is different, the CSI-RS configuration maybe considered to be different.

In order to distinguish (1) a CSI-RS configuration to which a CSI-RSconfiguration number is assigned from (2) a CSI-RS configuration whichvaries according to a CSI-RS configuration number, the number of CSI-RSports, and/or a subframe for which CSI-RSs are configured, the latterCSI-RS configuration (2) will be referred to as a CSI-RS resourceconfiguration, and the former CSI-RS configuration (1) will be referredto as a CSI-RS configuration or a CSI-RS pattern.

When the eNB indicates a CSI-RS resource configuration to a UE, the eNBmay transmit to the UE information about the number of antenna portsused for transmission of CSI-RSs, a CSI-RS pattern, a CSI-RS subframeconfiguration ICSI-RS, a UE assumption on reference PDSCH transmissionpower for CSI feedback, Pc, a zero power (ZP) CSI-RS configuration list,a ZP CSI-RS subframe configuration, and so on.

The index of a CSI-RS subframe configuration, ICSI-RS is informationthat specifies a subframe configuration periodicity TCSI-RS foroccurrence of CSI-RSs, and a subframe offset ΔCSI-RS. [Table 10] belowlists exemplary CSI-RS subframe configuration indexes, ICSI-RS accordingto TCSI-RS and ΔCSI-RS.

TABLE 10 CSI-RS- CSI-RS periodicity CSI-RS subframe SubframeConfigT_(CSI-RS) offset Δ_(CSI-RS) I_(CSI RS) (subframes) (subframes) 0-4   5I_(CSI-RS) 5-14 10 I_(CSI-RS)-5  15-34  20 I_(CSI-RS)-15 35-74  40I_(CSI-RS)-35 75-154 80 I_(CSI-RS)-75

Subframes satisfying [Equation 5] are CSI-RS subframes.(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=  [Equation 5]

A UE for which a transmission mode (TM) defined beyond 3GPP LTE-A (e.g.,TM9 or a newly defined TM) has been configured may perform channelmeasurement using CSI-RSs, and decode a PDSCH using UE-RSs.

A UE for which a Transmission Mode (TM) defined beyond 3GPP LTE-A (e.g.,TM9 or a newly defined TM) has been configured may perform channelmeasurement using CSI-RSs, and decode a PDSCH using UE-RSs.

1.7 Enhanced PDCCH (EPDCCH)

In cross-carrier scheduling (CCS) under a situation in which a pluralityof components carriers (CCs=(serving) cells) are aggregated in the 3GPPLTE/LTE-A system, one scheduled CC may be pre-configured to beDL/UL-scheduled only by one other scheduling CC (i.e., so that a DL/ULgrant PDCCH for the scheduled CC may be received). Basically, thescheduling CC may perform DL/UL scheduling for itself. In other words,an SS for a PDCCH that schedules a scheduling/scheduled CC in the CCSrelationship may exist in the control channel region of every schedulingCC.

Meanwhile, the LTE system allocates the first n (n<=4) OFDM symbols ofeach subframe to transmission of physical channels, PDCCH, PHICH, andPCFICH carrying control information and allocates the other OFDM symbolsof the subframe to PDSCH transmission in an FDD DL carrier or TDD DLsubframes. The number of OFDM symbols used for transmission of controlchannels in each subframe may be indicated to UEs, dynamically on aphysical channel such as the PCFICH or semi-statically by RRC signaling.

A physical channel used for DL/UL scheduling and transmission of varioustypes of control information, PDCCH has limitations such as transmissionin limited OFDM symbols in the LTE/LTE-A system. Therefore, an extendedPDCCH (i.e., EPDCCH) multiplexed more freely with a PDSCH in frequencydivision multiplexing (FDM)/time division multiplexing (TDM) may beintroduced, instead of a control channel such as the PDCCH transmittedin OFDM symbols separate from PDSCH symbols. FIG. 11 is a viewillustrating exemplary multiplexing of the legacy PDCCH, the PDSCH, andthe EPDCCH in the LTE/LTE-A system.

1.8 Synchronization Signal

A synchronization signal (SS) includes a primary synchronization signal(PSS) and a secondary synchronization signal (SSS). The SS is a signalused for establishing synchronization between a UE and an eNB andperforming cell search.

FIG. 12 is a view illustrating an exemplary frame structure showing aposition for transmitting a synchronization signal. In particular, FIG.12(a) shows a frame structure for SS transmission in a system using aCyclic Prefix (CP), and FIG. 12 (b) shows a frame structure for SStransmission in a system using an extended CP.

The SS is transmitted in a second slot in each of subframe 0 andsubframe 5 in consideration of a GSM frame length of 4.6 ms forfacilitation of inter-Radio Access Technology (inter-RAT) measurement.In this case, boundaries of a corresponding radio frame may be detectedthrough the SSS.

Referring to FIG. 12(a) and FIG. 12(b), the PSS is transmitted in thelast OFDM symbol of each of slot 0 and slot 5, and the SSS istransmitted in an OFDM symbol immediately before the OFDM symbol inwhich the PSS is transmitted. The SS can carry total 504 physical layercell IDs (physical cell IDs) through combinations of 3 PSSs and 168SSSs. In addition, the SS and a PBCH are transmitted within 6 RBs in themiddle of the system bandwidth, and thus a UE can detect or decode theSS and PBCH irrespective of a transmission bandwidth size.

A transmission diversity scheme for the SS uses a single antenna portonly. That is, a single antenna transmission scheme or a transmissionscheme transparent to a UE (e.g., PVS, TSTD, CDD, etc.) may be used.

1.8.1 Primary Synchronization Signal (PSS)

A Zadoff-Chu (ZC) sequence of length 63 is defined in the frequencydomain and the sequence is used as a sequence for the PSS. The ZCsequence can be defined according to Equation 6.

$\begin{matrix}{{d_{u}(n)} = e^{{- j}\frac{\pi\;{{un}{({n + 1})}}}{N_{ZC}}}} & \lbrack {{Equation}\mspace{14mu} 6} \rbrack\end{matrix}$

In Equation 6, NZC indicates the length of the ZC sequence, 63 and du(n)indicates the PSS sequence in accordance with a root index, u. In thiscase, a sequence element corresponding to a direct current (DC)subcarrier, n=31 is punctured.

In order to facilitate designing a filter for performingsynchronization, 9 remaining subcarriers among 6 RBs (i.e., 72subcarriers) in the middle of the bandwidth are always set to 0 and thentransmitted. To define total 3 PSSs, u may have the values of 25, 29 and34 in Equation 2 (i.e., u=25, 29 and 34). In this case, since u=29 andu=34 are in a conjugate symmetry relation, two correlations may besimultaneously performed. Here, the conjugate symmetry means a relationin Equation 3 below. A one-shot correlator for u=29 and u=34 can beimplemented using conjugate symmetry characteristics, and the totalamount of calculation can be reduced by about 33.3%.d _(u)(n)=(−1)^(n)(d _(N) _(ZC) _(-u)(n))*, when N _(ZC) is even number.d _(u)(n)=(d _(N) _(ZC) _(-u)(n))*, when N _(ZC) is oddnumber.  [Equation 7]

1.8.2 Secondary Synchronization Signal (SSS)

The SSS is generated by interleaving and concatenating two m-sequenceseach of length 31. In this case, 168 cell group IDs can be distinguishedby combining the two sequences. As a sequence for the SSS, them-sequence has a robust property in a frequency-selective environment.In addition, the amount of calculation can be reduced by applyinghigh-speed m-sequence transformation using Fast Hadamard Transform.Moreover, to reduce the amount of calculation of a UE, it is proposedthat the SSS is composed of two short codes.

FIG. 13 is a view illustrating a method for generating a secondarysynchronization signal.

Referring to FIG. 13, it can be seen that two sequences defined in thelogical domain are interleaved and mapped in the physical domain. Forexample, two m-sequences used for generating an SSS code may berespectively defined as S1 and S2. In this case, if an SSS in subframeindex 0 carries a cell group ID through a combination of (S1, S2) and anSSS in subframe index 5 is transmitted by being swapped as (S2, S1), itis possible to distinguish between boundaries of a 10 ms frame. In thiscase, a generation polynomial of x5+x2+1 may be used for the SSS code,and total 31 codes may be generated through different circular shifts.

In order to improve reception performance, two different PSS-basedsequences are defined and scrambled into the SSS. In this case,scrambling may be performed on S1 and S2 using different sequences.Thereafter, an S1-based scrambling code is defined, and then scramblingis performed on S2. In this case, the SSS code is swapped every 5 ms buta PSS-based scrambling code is not swapped. The PSS-based scramblingcode is defined based on an m-sequence generated from the generationpolynomial of x5+x2+1 by applying six cyclic shift schemes according toPSS indices, and S1-based scrambling code is defined based on anm-sequence generated from a polynomial of x5+x4+x2+x1+1 as eight cyclicshift versions according to S1 indices.

2. Narrowband Internet of Things (NB-IoT)

2.1 NB-IoT Overview

The narrowband (NB) LTE is a system for supporting low complexity andpower consumption using a system bandwidth corresponding to one PRB,which is defined in the LTE system. As a communication scheme, the NBLTE can be used to implement IoT by supporting devices in a cellularsystem like machine-type communication (MTC). That is, the NB LTE systemcan be referred to as an NB-IoT system.

Since the NB-IoT system use the same OFDM parameters includingsubcarrier spacing as in the LTE system, one PRB in the legacy LTE bandis allocated for the NB-LTE without additional allocation of bands. Thatis, the NB-IoT system has advantages in that frequencies can beefficiently used.

In the NB-LTE system, physical downlink channels are defined as anM-PSS/M-SSS, an M-PBCH, an M-PDCCH/M-EPDCCH, an M-PDSCH, etc. or anNB-PSS/NB-SSS, an NB-PBCH, an NB-PDCCH/NB-EPDDCH, an NB-PDSCH, etc. Todistinguish the physical downlink channels of the NB-LTE system fromphysical channels of the LTE system, ‘M-’ or ‘NB-’ can be added.

Embodiments of the present disclosure as described below relate to a PSSand an SSS which are applied to an NB-IoT system. Therefore, althoughNPSS, MPSS or NB-PSS is written shortly as PSS, the terms areinterchangeably used in the same meaning. In addition, although NSSS,MSSS or NB-SSS is written shortly as SSS, the terms are interchangeablyused in the same meaning.

Further, in embodiments of the present disclosure, one PRB includes apair of RBs, for which the description of FIGS. 2 and 3 may be referredto. For example, one RB may include 7 OFDM symbols by 12 subcarriers.

2.2 Golay Sequence

Golay complementary sequences are pairs of binary codes belonging tosignals called complementary pairs, which include two codes of the samelength n. The Golay sequences have auto-correlation functions withside-lobes equal in magnitude but opposite in sign. Summing theauto-correlation functions up results in a composite auto-correlationfunction with a peak of 2n and zero side-lobes.

There are several different algorithms for generating Golay pairs. Forexample, DOKOVIC described a method of calculating Golay sequences.Variables a_(i) and b_(i) (i=1, 2, . . . , n) are the elements of twon-long complementary sets, which are equal to either +1 or −1. Herein,A=a₁, a₂, . . . , a_(n), and B=b₁, b₂, . . . , b_(n).

The ordered pair (A;B) are Golay sequences of length n if the following[Equation 8] is satisfied, and satisfy the following [Equation 9] in theLaurent polynomial ring Z[x,x⁻¹].A(x)=a ₁ +a ₂ x+ . . . +a _(n) x ^(n-1)B(x)=b ₁ +b ₂ x+ . . . +b _(n) x ^(n-1)  [Equation 8]A(x)A(x ⁻¹)+B(x)B(x ⁻¹)=2n  [Equation 9]

The auto-correlation functions N_(A) and N_(B) corresponding to thesequences A and B respectively are defined by the following expressions.

$\begin{matrix}{{{N_{A}(j)} = {\sum\limits_{i \in Z}{a_{i}a_{i + j}}}}{{N_{B}(j)} = {\sum\limits_{i \in Z}{b_{i}b_{i + j}}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

Herein, if k∉(1, . . . , n), a_(k)=0. [Equation 9] may be replaced withthe sum of N_(A) and N_(B), which may be expressed as the following[Equation 11].

$\begin{matrix}{{{N_{A}(j)} + {N_{B}(j)}} = \{ \begin{matrix}{{2N},} & {j = 0} \\{0,} & {j \neq 0}\end{matrix} } & \lbrack {{Equation}\mspace{14mu} 11} \rbrack\end{matrix}$

In [Equation 11], the sum of both autocorrelation functions is 2N at j=0and zero otherwise.

Budision described the recursive method for constructing Golaysequences, presented below.a ₀(i)=δ(i),b ₀(i)=δ(i)a _(n)(i)=a _(n-1)(i)+b _(n-1)(i−2^(n-1))b _(n)(i)=a _(n-1)(i)+b _(n-1)(i−2^(n-1))  [Equation 12]

In [Equation 12], variables a(i) and b(i) may be the elements of twocomplementary sequences with elements 1 and −1 of length 2^(n)\, wherei=0, 1, . . . , 2^(n-1). In addition, δ(i) is a Kronecker deltafunction. [Equation 12] describes generation of new elements of thesequences in each step by concatenating elements a_(n)(i) and b_(n)(i)of length n.

3. Method for Generating PSS in NB-IoT System

FIG. 14 is a view illustrating a method for transmitting a PSS in aspecific subframe in an NB-IoT system.

In the NB-IoT system, a BS transmits a PSS in a plurality of OFDMsymbols. Herein, a sequence transmitted in the OFDM symbols may beconfigured so that the same sequence is repeatedly transmitted in theOFDM symbols (S1410), and each OFDM symbol is multiplied by a specificcover sequence (S1420).

That is, the BS generates a plurality of PSSs by using the same sequence(e.g., a Golay sequence or ZC sequence) in order to transmit the PSSs inthe plurality of OFDM symbols. Then, the BS may transmit the generatedsame PSSs in the plurality of OFDM symbols (S1430).

On the assumption of a bandwidth of one PRB and a subcarrier spacing of15 KHz in the NB-IoT system, the maximum length of a sequencetransmittable in one OFDM symbol is 12. For the convenience ofdescription, the following description is given with the appreciationthat the system bandwidth is one PRB, and the subcarrier spacing is 15KHz.

Typically, a receiver (i.e., a UE) is configured to process a PSS in thetime domain in consideration of computation complexity involved indetection. To acquire time/frequency synchronization by the PSS, the UEcorrelates a PSS sequence by applying a sliding window.

FIG. 15 is a view illustrating a method for generating a PSS in theNB-IoT system.

With reference to FIG. 14, the method for generating a PSS will bedescribed again in FIG. 15.

The BS generates a first sequence of length M. In order to transmit aPSS in N OFDM symbols included in one subframe, the BS repeats the firstsequence of length M N times. Or the BS may repeatedly use asystem-preset first sequence N times (S1510).

To generate a PSS sequence, the BS may multiply the N first sequences bya cover sequence c(n) of a length equal to the length of OFDM symbolscarrying PSSs. Herein, each time the BS generates a PSS sequence, the BSmay generate the cover sequence c(n) or use a system-preset coversequence c(n). The cover sequence may be referred to as a secondsequence. The reason for multiplying the cover sequence is to facilitatedetection of a peak value for a PSS, when the UE detects the PSS.

In FIG. 14, the first sequence of length M is mapped to the subcarriersof one OFDM symbol in one RB. The BS fills ‘0’ in subcarriers (i.e.,REs) to which the first sequence is not allocated in a specific OFDMsymbol carrying a PSS. In addition, the N OFDM symbols may be OFDMsymbols except for a control region in one subframe. For example, if thecontrol region of one subframe is 3 OFDM symbols, N may be set to 11.

The BS may map the generated PSS sequences to REs. Herein, the BS maymap the same N PSS sequences in the OFDM symbols except for the controlregion of the subframe (S1530).

The BS may transmit N PSSs in the fifth subframe of every radio frame(S1540).

In the PSS transmission structure of FIG. 14, the same sequence istransmitted in each OFDM symbol, and thus a relatively large correlationvalue may result with a periodicity of an OFDM symbol length. Herein, ifthe condition of [Equation 11] for Golay complementary sequences isused, the output period of a relatively large correlation value may beincreased, thereby improving correlation characteristics. The BS mayfurther improve the correlation characteristics by applying a coversequence to each OFDM symbol in order to generate a PSS. Methods fortransmitting a PSS by using Golay complementary sequences as firstsequences are given as follows.

3.1 First Method for Generating PSS

The first method for generating a PSS is to arrange a pair of Golaycomplementary sequences alternately in respective OFDM symbols. Forexample, if the number of OFDM symbols carrying PSSs is 6 (N=6), the BSmay transmit a(n) in OFDM symbol #1, and b(n) in OFDM symbol #2. Herein,c(n) may be applied by taking a length of 6 from an m-sequence of length7.

In addition, it is preferred that the number of OFDM symbols carryingPSSs is an even number. If it is assumed that Golay complementarysequences are binary sequences, the possible lengths of the sequencesmay be 2^(a), 10^(b), 26^(c), and/or 2^(a)*10^(b)*26^(c) (a, b and c are0 or larger integers). If only 12 resources are available in one OFDMsymbol, the possible length for the Golay sequences may be 10. In anembodiment of a Golay complementary sequence pair [a(n), b(n)],a(n)=[11−1−1111−11−1] and b(n)=[11111−11−1−11]. The BS may transmit theOFDM symbols with ‘0’ filled in the REs of subcarriers to which a PSSsequence is not allocated.

If non-binary Golay complementary sequences are assumed, a sequence pairmay exist without a length limit in generating PSSs. Therefore, the BSmay arrange a sequence pair of length 12, a(n) and b(n) in OFDM symbolsin the same manner. Correlation characteristics for a complementarysequence pair of length n, a(n) and b(n), and various c(n) patterns areillustrated in FIG. 16.

FIG. 16 is a view illustrating correlation characteristics according tocover code patterns required for generating a PSS.

FIG. 16 illustrates correlation characteristics according to acomplementary sequence pair a(n)=[11−1−1111−11−1] andb(n)=[11111−11−1−11], and various cover code patterns. That is, FIG.16(a) illustrates a case where the cover sequence pattern is [1111−1−1],FIG. 16(b) illustrates a case where the cover sequence pattern is[11−1−111], FIG. 16(c) illustrates a case where the cover sequencepattern is [1−1−1111], and FIG. 16(d) illustrates a case where the coversequence pattern is [1−111−11].

In FIG. 16, it is assumed that the length of a cover sequence is 6. Thisimplies that a synchronization sequence used to generate PSSs isrepeatedly generated 6 times. If a synchronization sequence is generatedrepeatedly N times, the length of a cover sequence may also be set to N.

In another aspect of the first method, if the BS transmits PSSs in anodd number of OFDM symbols, the PSSs may be transmitted by transmittingone sequence in a sequence pair once more. For example, if N=7, the BSmay arrange Golay sequences in the order of a(n)b(n)a(n)b(n)a(n)b(n)a(n)in the OFDM symbols.

3.2 Second Method for Generating PSS

The BS may generate PSSs by arranging a pair of Golay complementarysequences in one OFDM symbol.

In one method, the BS may generate sequences corresponding to the halvesof one OFDM symbol, and arrange the sequences in the OFDM symbol. Forexample, it may be assumed that a PSS is transmitted repeatedly in sixOFDM symbols (N=6). Herein, the BS may generate non-binary Golaycomplementary sequences of length 6, a(n) and b(n), allocate a(n) to onehalf of the available REs of one OFDM symbol, and allocate b(n) to theother half of the available REs of the OFDM symbol. Herein, as a methodfor allocating a synchronization sequence to REs, the BS may allocatea(n) to the former half of REs of an OFDM symbol and b(n) to the latterhalf of the REs.

In another method, the BS may superpose a(n) and b(n) in one OFDMsymbol. For example, if a PSS is transmitted repeatedly in 6 OFDMsymbols (N=6), the BS may generate binary/non-binary Golay complementarysequences of length 10 or 12, and calculate a(n)+b(n), for transmission.

3.3 Third Method for Generating PSS

The BS may arrange and transmit L (L>2) or more Golay complementarysequences. Preferably, the number of OFDM symbols carrying PSSssatisfies the condition of a multiple of L. For example, if L=3 and N=6,the BS may sequentially arrange and transmit Golay complementarysequences of length 10 or 12, la(n), lb(n), and lc(n) in OFDM symbols.That is, the BS may arrange the first sequences in the order of la(n),lb(n), lc(n), la(n), lb(n), and lc(n) to generate PSSs, apply a coversequence c(n) to the first sequences, and transmit the PSSs.

3.4 Method for Generating PSS by ZC Sequence

In the afore-described Sections 3.1 to 3.3, a Golay sequence is used asa first sequence in order to generate a PSS. Now, a description will begiven of methods for using a ZC sequence as a first sequence.

The BS may use a ZC sequence of length 11 to generate a PSS. The ZCsequence of length 11 may be defined as the following [Equation 13].

$\begin{matrix}{{{Z(k)} = {\exp( \frac{{- j}\; u\;\pi\;{k( {k + 1} )}}{11} )}},{u = 1},2,\ldots\mspace{14mu},10,{k = 0},1,\ldots\mspace{14mu},10} & \lbrack {{Equation}\mspace{14mu} 13} \rbrack\end{matrix}$

In [Equation 13], u is a root index for the ZC sequence. The BS mayselect two ZC sequences Z₁(k) and Z₂(k) having different root indexes,and map the selected ZC sequences to OFDM symbols. In addition, the BSmay apply a cover code (or cover sequence) c(k) to each of the OFDMsymbols.

On the assumption that the number of OFDM symbols carrying PSSs is 11,the BS may arrange Z₁(k) and Z₂(k) in the OFDM symbols in the followingmethods. In the following methods, as the number of OFDM symbols inwhich one sequence is arranged contiguously is smaller, PSS detectionperformance may be improved, and as the number of OFDM symbols in whichone sequence is arranged contiguously is larger, the computation volumeof a UE may be reduced in a specific detection method. Accordingly, thenumber of OFDM symbols carrying PSSs may be in a trade-off relationship.

3.4.1 Method 1

The BS may arrange one ZC sequence (e.g., Z1(k)) successively in twoOFDM symbols, and the other ZC sequence (e.g., Z2(k)) in the followingtwo OFDM symbols. For example, the BS may arrange the ZC sequences inthe order of [Z1(k)Z1(k)Z2(k)Z2(k)Z1(k)Z1(k)Z2(k)Z2(k)Z1(k)Z1(k)Z2(k)]in OFDM symbols.

3.4.2 Method 2

The BS may arrange one ZC sequence (e.g., Z1(k)) successively in threeOFDM symbols and the other ZC sequence (e.g., Z2(k)) in the followingthree OFDM symbols. For example, the BS may arrange the ZC sequences inthe order of [Z1(k)Z1(k)Z1(k)Z2(k)Z2(k)Z2(k)Z1(k)Z1(k)Z1(k)Z2(k)Z2(k)]in OFDM symbols.

3.4.3 Method 3

The BS may arrange one ZC sequence (e.g., Z1(k)) successively in fourOFDM symbols, and the other ZC sequence (e.g., Z2(k)) in the followingfour OFDM symbols. For example, the BS may arrange the ZC sequences inthe order of [Z1(k)Z1(k)Z1(k)Z1(k)Z2(k)Z2(k)Z2(k)Z2(k)Z1(k)Z1(k)Z1(k)]in OFDM symbols.

3.4.4 Method 4

The BS may arrange one ZC sequence (e.g., Z1(k)) successively in fiveOFDM symbols, and the other ZC sequence (e.g., Z2(k)) in the followingfive OFDM symbols. For example, the BS may arrange the ZC sequences inthe order of [Z1(k)Z1(k)Z1(k)Z1(k)Z1(k)Z2(k)Z2(k)Z2(k)Z2(k)Z2(k)Z1(k)]in OFDM symbols.

3.4.5 Method 5

The BS may arrange one ZC sequence (e.g., Z1(k)) successively in sixOFDM symbols, and the other ZC sequence (e.g., Z2(k)) in the followingsix OFDM symbols. For example, the BS may arrange the ZC sequences inthe order of [Z1(k)Z1(k)Z1(k)Z1(k)Z1(k)Z1(k)Z2(k)Z2(k)Z2(k)Z2(k)Z2(k)]in OFDM symbols.

3.5 Cover Sequence

A cover sequence or cover code c(k) may contribute much to improvementof the correlation characteristics of a PSS sequence. That is, the UEdetects a peak value by correlation to receive a PSS signal, and thecover sequence may facilitate detection of the peak value. The following[Equation 14] represents an exemplary set of cover sequences.c(k)={[1,1,1,1,−1,1,−1,1,1,−1,1],[1,1,1,−1,−1,−1,−1,−1,1,−1,1],[1,−1,1,1,−1,1,−1,1,1,1,1],[1,−1,1,−1,−1,−1,−1,−1,1,1,1],or [1,−1,1,1,1,1,1,1,−1,−1,−1]}  [Equation 14]

In [Equation 14], c(k) represents code covers or cover sequences whichare optimal in terms of a minimum power sum of a second peak value and aside-lobe, when the BS selects two of the ZC sequences of [Equation 13]and configure the selected ZC sequences as illustrated in FIG. 14.Herein, it is assumed that the root indexes of the ZC sequences are 5and/or 6, and the ZC sequences are alternately transmitted in OFDMsymbols.

Cover codes obtained by exchanging the signs +/− in the set of coversequences c(k) in [Equation 14] also have the same performance.

In the foregoing embodiments and later-described embodiments of thepresent disclosure, an M sequence or a sequence of length M may be a ZCsequence, a Golay sequence, or the like. That is, unless specifiedotherwise, an M sequence or a sequence of length M may mean a ZCsequence, a Golay sequence, or the like.

4. Methods for Generating SSS in NB-IoT System

Methods for generating an SSS in the NB-IoT system will be describedbelow.

A UE may acquire time and frequency synchronization based on a receivedPSS, and detect a cell ID, the index of a subframe carrying an SSS, andother system information by detecting an SSS.

FIG. 17 is a view illustrating a method for transmitting an SSS in aspecific subframe in the NB-IoT system.

An SSS transmission structure may be configured as illustrated in FIG.17. To generate an SSS sequence, the BS may generate a sequence oflength M (or a first sequence) (S1710). In addition, to generate the SSSsequence, the BS may generate a scrambling sequence of length M (or asecond sequence) s(n) (S1720).

The BS may generate a sub-sequence (or a third sequence) by multiplyingthe first sequence by the second sequence (S1730).

In step S1730, the first sequence and the second sequence may bemultiplied element-wise. For example, if there are a set of firstsequences and a set of second sequences, a sub-sequence may be generatedby multiplying the elements of the respective sets.

Subsequently, the BS may map the generated sub-sequence in OFDM symbolsof a subframe, in which SSSs are transmitted (S1740).

Or, to transmit an SSS sequence in N OFDM symbols, the BS may divide thefirst sequence into sequences of length L (M>=L), arrange the sequencesof length L in the respective N OFDM symbols, and generate SSSs byapplying the scrambling sequence s(n) to the divided first sequences.For example, if M=72, L=12, and N=6, the BS may divide a first sequenceof length 72 into six sequences of length 12, and transmit the sixsequences respectively in six OFDM symbols.

FIG. 18 is a view illustrating a method for generating an SSS in aspecific subframe in the NB-IoT system.

In order to generate an SSS sequence, the BS generates a first sequenceof length M and a second sequence of length M (S1810 and S1820).

In embodiments of the present disclosure, a ZC sequence may be used asthe first sequence, and a scrambling sequence or a Hadamard sequence maybe used as the second sequence. The UE may derive a physical cell ID(PCI) and subframe position information from information included in thereceived first and second sequences.

The BS may generate a third sequence by using the first and secondsequences. The third sequence may be referred to as an SSS sequence or asub-sequence (S1830).

The BS may generate SSSs based on the third sequence. That is, the BSmay generate SSSs by allocating and mapping the third sequence to REs ofN OFDM symbols in a specific subframe (SF) (S1840).

The BS may transmit the SSSs in the N OFDM symbols (S1840).

Now, a description will be given of methods for designing and generatingan SSS in the NB-IoT system, which are applicable to FIGS. 17 and 18.

4.1 First Method for Generating SSS

The BS generates two ZC sequences of length M/2 (i.e., first sequences)(e.g., SSS1 and SSS2), and then generates a first sequence of length Mby concatenating the two ZC sequences. The root indexes of the ZCsequences may be fixed to a specific value. For example, root index umay be fixed to ‘1’.

The BS may represent information about a cell ID by a combination ofcyclic shift values (CS1 and CS2) for the generated two first sequences.Then, the BS may generate a scrambling sequence of length M (i.e., asecond sequence) by a function of information about a subframe carryingSSSs and system information. Subsequently, the BS may divide the firstsequence into N sequences of length L, and allocate the N sequences to NOFDM symbols.

For example, if M=72, L=12, and N=6, the BS generates two ZC sequences,using cyclic shift values representing a cell ID, and concatenates theZC sequences. That is, to transmit a PN sequence of length 128 based ona scrambling sequence of length c in six OFDM symbols, the BS may dividethe concatenated ZC sequence into sequences of length 12, and allocatethe sequences of length 12 to the respective OFDM symbols.

The scrambling sequence may be expressed as [Equation 15].c _(init) =N _(sys)2⁴ +N _(index) ^(subframe)  [Equation 15]

The BS may generate a scrambling sequence of length 72 by applying apredetermined offset to an m sequence of length 127 generated throughinitialization to system information (N_(sys)2⁴), subframe information(N_(index) ^(subframe)), and so one, as described in [Equation 15].Subsequently, the BS may multiply the generated scrambling sequence bythe concatenated ZC sequence.

In another method, the BS may generate an offset value for an m sequenceof length 127, which has been generated by initializing the scramblingsequence to any value (e.g., c_(init)=1), by means of a function ofsubframe information, system information, and so on, and then generate ascrambling sequence of length 72 based on the offset value.

If the offset value is larger than 55, the scrambling sequence isgenerated by counting to a beginning sequence in a cyclic shift manner.For example, the scrambling sequence may be generated in the manner ofs(k), . . . , s(127), s(1), . . . .

4.2 Second Method for Generating SSS

The BS generates a first sequence of length M by generating two Golaycomplementary sequences of length M/2 (e.g., SSS1 and SSS2) and thenconcatenating the Golay complementary sequences. Herein, the BS may useone Golay sequence of the Golay complementary sequence pair as SSS1 orSSS2, or allocate one of the Golay complementary sequences as SSS1 andthe other Golay complementary sequence as SSS2.

The BS may represent information about a physical cell ID by acombination of cyclic shift values (CS1 and CS2) for the generated twosequences. Then, the BS may generate a scrambling sequence of length Mby a function of information about a subframe carrying SSSs and systeminformation. Subsequently, the BS may divide the sequence of length L bythe number of OFDM symbols, N, and allocate the divided sequences to Nrespective OFDM symbols. The BS may allocate ‘0’ instead of an SSSsequence to a part of REs of the OFDM symbols in view of a limitation onthe length of the Golay complementary sequence pair according to acombination of M, L and N.

4.3 Third Method for Generating SSS

In another method for transmitting an SSS, the BS may consider thetransmission structure in FIG. 19.

FIG. 19 is a view illustrating another method for transmitting an SSS ina specific subframe in the NB-IoT system.

Referring to FIG. 19, the BS generates K first sequences of length M_(k)and K second sequences (or scrambling sequences) of length M_(k). Thelengths of the first sequences g_(k)(n) and the second sequencess_(k)(n) generated by the BS may be set to be equal. The BS may generatesub-sequences (or third sequences) by multiplying g_(k)(n) by s_(k)(n)element-wise, for transmission in OFDM symbols. Herein, the BS mayinsert ‘0s’ in remaining RE areas, when the sub-sequences are generatedaccording to the amount of data transmittable in each OFDM symbol.

If the amount of data transmittable in each OFDM symbol is ‘R’, thelength of a sequence transmittable in ‘N’ OFDM symbols is N*R,satisfying the relationship that N*R>=K*M_(k). Therefore, the number ofOFDM symbols carrying SSSs, N and an information transfer method mayvary according to k, g_(k)(n), and/or s_(k)(n).

In embodiments of the present disclosure, it is assumed that SSSs carry504 PCIs and information about the positions of eight subframes in whichSSSs are transmitted. Therefore, the BS preferably designs an SSSsequence so that a total of 4032 different hypotheses may bedistinguished. In addition, if M_(k) is different, the sequences havedifferent lengths, and thus correlation performance may be differentduring reception at a UE. Therefore, since the correlation performanceis determined by a smallest M_(k) value, it is preferred that thesequences have the same length M_(k).

4.3.1 K=2

On the assumption that the BS generates two sequences of the samelength, sequences of length 64 are needed (64*64=4096>4032) in order toallow a UE to distinguish 4032 hypotheses by receiving an SSS. Thesequences of length 64, g_(k)(n) (k=1, 2) may be selected from sequencesproposed in the following options.

Option 1) Walsh-Hadamard Sequences of Length 64

H₆₄ ^(u) may represent a u^(th) column or row (u=1, . . . , 64) of a64×64 Walsh-Hadamard matrix.

Option 2) Golay Complementary Sequences of Length 64

If sequences of length L, a_(n) and b_(n) satisfy the property of aGolay complementary sequence pair, sequences of length 2L, a_(n)′=[a_(n)b_(n)] and b_(n)′=[a_(n)−b_(n)] also satisfy the property of a Golaycomplementary sequence pair. Therefore, since a₁=[11] and b₁[1−1]satisfy the complementary property, the BS may generate a pair of Golaysequences of length 64, using a₁ and b₁ in a recursive manner such asthe method for generating an SSS sequence of length 2L. If the BSgenerates 32 different Golay sequence pairs, the BS may generate a 64×64matrix. G₆₄ ^(u) represents a u^(th) column or row (u=1, . . . , 64) ofsuch a 64×64 matrix.

Option 3) Sequences of Length 64 Each Obtained by Adding ‘0’ at anyPosition of an m-Sequence of Length 63

The BS may generate a 64×64 matrix with 64 sequences of length 64generated by 64 cyclic shifts. M₆₄ ^(u) represents a u^(th) column orrow (u=1, . . . , 64) of such a 64×64 matrix.

Option 4) ZC Sequences of Length 67

The BS may generate a 64×67 matrix with 64 sequences of length 67generated based on 64 root indexes for a ZC sequence of length 67. Or,the BS may generate a 64×66 or 64×64 matrix with sequences of length 66or 64 by puncturing sequences of length 67. Herein, Z₆₇ ^(u)/Z₆₆^(u)/Z₆₄ ^(u) represent a sequence of length 67/66/64 generated based onroot index u.

Therefore, a PCI and subframe position information may be transmitted bya combination of a u^(th) column or row and a v^(th) column or row of a64×64 matrix as proposed in the above options. For example, acombination of (u, v) (u, v=1, 2, . . . , 64) may carry a PCI andsubframe position information.

4.3.2 Method for Generating SSS Sequence for K=2

Since the scrambling sequence (i.e., the second sequence) s_(k)(n) hasthe same length as the first sequence g_(k)(n), the scrambling sequenceis a sequence of length 64. Therefore, the BS may design a modifiedm-sequence generated in the method of option 3) as the first sequenceg_(k)(n). If the first sequence g_(k)(n) is a modified m-sequence as inoption 3), the scrambling sequence s_(k)(n) is preferably generated by adifferent generator polynomial from that of g_(k)(n).

Since it is preferred to design the scrambling sequence s_(k)(n) in amanner that reduces interference from an SSS transmitted from a neighborcell, the BS may generate a different sequence by defining a cyclicshift value according to a PCI. Hereinbelow, methods for generating anSSS sequence by a BS will be described.

4.3.2.1 Method 1

The BS may generate an SSS sequence in the form of[g1(n)*s1(n)g2(n)*s2(n)]. Because the scrambling sequence s_(k)(n) isPCI-based, a receiver needs 504*2 correlation operations to acquire aPCI and subframe position information.

4.3.2.2 Method 2

The BS may generate an SSS sequence in the form of[g1(n)*s1(n)g2(n)*s1(n)]. Because the scrambling sequence s_(k)(n) isPCI-based, a receiver (i.e., a UE) needs 504*2 correlation operations toacquire a PCI and subframe position information.

4.3.2.3 Method 3

The BS may generate an SSS sequence in the form of [g1(n)g2(n)*s1(n)].Because the scrambling sequence s_(k)(n) is determined by a PCI andaffects only g2(n), a receiver needs 64+504 correlation operations.

The length of an SSS sequence generated in the above methods is 128(=64*2). Accordingly, at least 11 OFDM symbols (N=11) are required totransmit the SSS sequence. To divide the SSS sequence on an OFDM symbolbasis, the BS may transmit a beginning sequence of length 64 in firstsix OFDM symbols, and the following sequence of length 64 in thefollowing six OFDM symbols.

[Table 11], [Table 12], and [Table 13] are given to describe u and vvalues according to PCIs and subframe positions, and cyclic shift valuesp1 and p2 for a scrambling sequence in relation to the SSS sequencegeneration methods.

[Table 11] illustrates u and v values according to PCIs and subframepositions, and cyclic shift values p1 and p2 for a scrambling sequencein the first method for generating an SSS, described in Section 4.3.2.1.

TABLE 11 SF SF PCI position u v p1 p2 PCI position u v p1 p2 0 0 1 1 0 01 0 1  9 0 1 0 1 1 2 0 0 1 1 1 10 0 1 0 2 1 3 0 0 2 0 1 17 0 2 0 3 1 4 00 2 1 1 18 0 2 0 4 1 5 0 0 3 0 1 25 0 3 0 5 1 6 0 0 3 1 1 26 0 3 0 6 1 70 0 4 0 1 33 0 4 0 7 1 8 0 0 4 1 1 34 0 4 . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . .

[Table 12] illustrates u and v values according to PCIs and subframepositions, and cyclic shift values p1 and p2 for a scrambling sequencein the second method for generating an SSS, described in Section4.3.2.2.

TABLE 12 PCI SF position u v p1 PCI SF position u v p1 0 0 1 1 0 1 0 1 9 1 0 1 1 2 0 1 1 1 10 1 0 2 1 3 0 2 0 1 17 2 0 3 1 4 0 2 1 1 18 2 0 41 5 0 3 0 1 25 3 0 5 1 6 0 3 1 1 26 3 0 6 1 7 0 4 0 1 33 4 0 7 1 8 0 4 11 34 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[Table 13] illustrates u and v values according to PCIs and subframepositions, and cyclic shift values p1 and p2 for a scrambling sequencein the third method for generating an SSS, described in Section 4.3.2.3.

TABLE 13 PCI SF position u v p1 PCI SF position u v p1 0 0 1 1 0 1 0 1 9 1 0 1 1 2 0 1 1 1 10 1 0 2 1 3 0 2 0 1 17 2 0 3 1 4 0 2 1 1 18 2 0 41 5 0 3 0 1 25 3 0 5 1 6 0 3 1 1 26 3 0 6 1 7 0 4 0 1 33 4 0 7 1 8 0 4 11 34 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3.3 Other Methods for Generating SSS Sequence for K=2

Other methods for generating an SSS sequence by a BS will be describedbelow. 9 bits are required to represent 504 PCIs, and 3 bits arerequired to represent 8 subframe positions. That is, the BS needs atotal of 12 bits to generate an SSS sequence, and the 12 bits may beexpressed as {p11, p10, . . . , p0}. Herein, p11 is a most significantbit (MSB) and p0 is a least significant bit (LSB).

That is, the SSS sequence may be represented as PCI_(b)*2³+SF_(b).Herein, PCI_(b) is a binary representation of a PCI, and SF_(b) is abinary representation of a subframe position. An SSS sequence obtainedby interleaving {p11, p10, . . . , p0} may be represented as {q11, q10,. . . , q0}. Herein, an SSS sequence may be generated by using a decimalrepresentation of {q11, . . . , q6} as the index of a u value and [q5, .. . , q0] as the index of a v value. For example, if {q11, . . . , q6}is {1, 0, 0, 1, 1, 0}, 1001102=42 and thus 42 may be used as the indexof u.

It is preferred to design an interleaver such that the bits representinga PCI and subframe position information may affect both u and v indexes.For example, a PCI is 9 bits, thus affecting both u and v indexes, andthe interleaver is preferably designed so that all of bits {p2, p1, p0}representing a subframe position may not be mapped to {q11, . . . , 16}or {q5, . . . , q0}.

[Table 14] illustrates an exemplary interleaver for mapping u and vindexes according to a PCI and a subframe position.

TABLE 14 Original p11 p10 p9 p8 p7 p6 p5 p4 p3 p2 p1 p0 sequence Inter-q11 q10 q9 q8 q7 q0 q5 q4 q3 q2 q1 q6 leaved sequence

The SSS sequence generated in this manner has a length of 128 (=64*2).Therefore, the BS needs at least 11 OFDM symbols (N=11) to transmit theSSS sequence. To divide the SSS sequence on an OFDM symbol basis, the BSmay transmit a beginning sequence of length 64 in first six OFDMsymbols, and the following sequence of length 64 in the following sixOFDM symbols.

4.3.2 K=3

On the assumption that the BS generates three sequences of the samelength, sequences of length 16 are needed (64*64*64=4096>4032) in orderto allow a UE to distinguish 4032 hypotheses by receiving an SSS. Thesequences of length 16, g_(k)(n) (k=1, 2, 3) may be selected fromsequences proposed in the following options. Or the BS may considersequences of length 32, g_(k)(n) (k=1, 2, 3) to improve the correlationperformance of a UE.

Option 1) Walsh-Hadamard Sequences of Length 16 or 32

H₁₆ ^(u)/H₁₂ ^(u) represents a u^(th) column or row (u=1, . . . , 16/32)of a 16×16 or 32×32 Walsh-Hadamard matrix.

Option 2) Golay Complementary Sequences of Length 16 or 32

If sequences of length L, a_(n) and b_(n) satisfy the property of aGolay complementary sequence pair, sequences of length 2L, a_(n)′=[a_(n)b_(n)] and b_(n)′=[a_(n), −b_(n)] also satisfy the property of a Golaycomplementary sequence pair. Therefore, since a₁=[11] and b₁[1−1]satisfy the complementary property, the BS may generate a pair of Golaysequences of length 16 or 32, using a₁ and b₁ in a recursive manner suchas the method for generating an SSS sequence of length 2L. If the BSgenerates 32 different Golay sequence pairs, the BS may generate a 64×64matrix. G₁₆ ^(u)/G₃₂ ^(u) represents a u^(th) column or row (u=1, . . ., 16/32) of such a 16×16 or 32×32 matrix.

Option 3) Sequences of Length 16 or 32 Each Obtained by Adding ‘0’ atany Position of an m-Sequence of Length 15 or 31

The BS may generate a 16×16 or 32×32 matrix with 16 or 32 sequences oflength 16 or 32 generated by 16 or 32 cyclic shifts. M₁₆ ^(u)/M₃₂ ^(u)represents a u^(th) column or row (u=1, . . . , 16/32) of such a 16×16or 32×32 matrix.

Option 4) ZC Sequences

The BS may generate a 16×17 or 30×31 matrix with 16 or 30 secondsequences of length 17 or 31 generated based on 16 or 30 root indexesfor a ZC sequence of length 17 or 31.

Or, the BS may generate a 16×17 or 16×16 matrix with second sequences oflength 16 by puncturing first sequences of length 17. Herein Z₁₇^(u)/Z₁₆ ^(u)/Z₃₁ ^(u) represents a sequence of length 17, 16 or 31generated based on root index u.

Therefore, a PCI and subframe position information may be transmitted bya combination of a u^(th) column or row, a v^(th) column or row, and aw^(th) column or row of a 16×16 or 32×32 matrix as proposed in the aboveoptions. That is, the BS may transmit a PCI and subframe positioninformation by an SSS sequence generated by a combination of (u, v, w)(u, v=1, 2, . . . , 16/32).

As in the case where K=2, a scrambling sequence is also determinedaccording to a PCI in the case where K=3, thereby reducing influencefrom an SSS transmitted from a neighbor cell. Accordingly, as in thecase where K=2, (u, v, w, p1, p2, p3) values may be defined as listed inthe afore-described [Table 11] to [Table 14] in the case where K=3.Herein, p1, p2 and p3 represent cyclic shift values for the scramblingsequence sk(n).

Since the total length of an SSS sequence is 48 (=16*3) or 96(32*3), theSSS sequence may be transmitted in 5 or 9 OFDM symbols. If the SSSsequence is to be transmitted in 9 OFDM symbols, it is preferred toavoid OFDM symbols carrying CRSs. In the case where all symbols carryingCRSs cannot be avoided, it is preferred to avoid OFDM symbols carryingCRSs in antenna port 2 with priority.

For K=K1 (K1 is an integer larger than 3), the BS may also transmit aPCI and subframe position information by generating an SSS sequence inthe same manner as for the afore-described cases where K=2 and 3.

4.4 Fourth Method for Generating SSS

Now, a description will be given of methods for designing an SSSsequence, when the number of hypotheses to be distinguished by SSSs is504, 1008 or 2016 smaller than 4032.

4.4.1 Method 1

If the number of OFDM symbols that the BS uses to transmit an SSS is setto 11, an SSS sequence length of 132 bits is available. Therefore, theBS may transmit an SSS sequence by concatenating two Hadamard sequencesof length 64.

504, 1008 or 2016 pieces of information may be represented by acombination of row or column indexes of a 64×64 Hadamard matrix.Accordingly, the BS may generate an SSS sequence, using two Hadamardsequences corresponding to corresponding column or row indexes.

If a UE is to distinguish 504 hypotheses, the 504 (<32*16=512)hypotheses may be distinguished by selecting 32 row/column indexes and16 row/column indexes from a Hadamard matrix. In the case of 1008hypotheses, the hypotheses may be distinguished by selecting 32row/column indexes and 32 row/column indexes. In the case of 2016hypotheses, the hypotheses may be distinguished by selecting 64row/column indexes and 32 row/column indexes. Herein, the BS maymultiply the sequence by a scrambling sequence of the same length, andtransmit the multiplied sequence, and the scrambling sequence may beobtained by adding 0 to an m-sequence of length 63.

4.4.2 Method 2

If the number of OFDM symbols used to transmit an SSS is 6, a sequencelength of 72 bits is available. Therefore, the BS may transmitinformation by concatenating two Hadamard sequences of length 32.

The BS represents 504 pieces of information by a combination of row orcolumn indexes of a 32×32 Hadamard matrix, and transmits two Hadamardsequences corresponding to corresponding column or row indexes. If a UEis to distinguish 504 hypotheses, the 504 (<32*16=512) hypotheses may bedistinguished by selecting 32 row/column indexes and 16 row/columnindexes from a Hadamard matrix. Herein, the sequence may be multipliedby a scrambling sequence of the same length, and transmitted, and thescrambling sequence may be obtained by adding 0 to an m-sequence oflength 31.

4.4.3 Method 3

If the number of OFDM symbols used to transmit an SSS is 7, a sequencelength of 84 bits is available. Therefore, the BS represents 504 or 1008pieces of information by a combination of row or column indexes of a40×40 Hadamard matrix, and transmit two Hadamard sequences correspondingto corresponding row or column indexes.

If a UE is to distinguish 504 hypotheses, the BS may distinguish the 504(<23*23=529) hypotheses by selecting 23 row/column indexes and 23row/column indexes from a 40×40 Hadamard matrix.

If a UE is to distinguish 1008 hypotheses, the BS may distinguish the1008 hypotheses (<32*32=1024) by selecting 32 row/column indexes.Herein, the BS may multiply the sequence by a scrambling sequence of thesame length, and transmit the multiplied sequence, and the scramblingsequence may be a sequence of length 40 obtained by puncturing 23 bitsin an m-sequence of length 63. In this case, the BS may match to 84 bitsby 4-bit zero padding.

4.4.4 Method 4

If the BS uses 9 OFDM symbols to transmit an SSS, an SSS sequence lengthof 108 bits is available. Therefore, the BS represents 504, 1008 or 2016pieces of information by a combination of row or column indexes of a52×52 Hadamard matrix, and transmit two Hadamard sequences correspondingto corresponding row or column indexes.

If a UE is to distinguish 504 hypotheses, the BS may distinguish the 504(<23*23=529) hypotheses by selecting 23 row/column indexes and 23row/column indexes from a 40×40 Hadamard matrix.

If a UE is to distinguish 1008 hypotheses, the BS may distinguish the1008 hypotheses (<32*32=1024) by selecting 32 row/column indexes.Herein, the BS may multiply the sequence by a scrambling sequence of thesame length, and transmit the multiplied sequence, and the scramblingsequence may be a sequence of length 52 obtained by puncturing 11 bitsin an m-sequence of length 63. In this case, the BS may match to 108bits by 4-bit zero padding.

4.5 Method for Transmitting Subframe Information

To reduce the amount of information transmitted in an SSS by the BS, itmay be configured that information about a subframe carrying the SSS isacquired from the SSS.

For example, if the BS transmits an SSS every 20 ms, the position of anSF carrying an SSS in the former 20 ms of 40 ms and the position of a SFcarrying an SSS in the latter 20 ms of 40 ms may be set to be differentor different sequences may be used for the SSSs, on the assumption of anequivalent SSS transmitted every 40 ms. Therefore, if a receiveracquires information by blind detection, only information about theposition of 40 ms has only to be transmitted as information to betransmitted in an SSS. The resulting decreased amount of information tobe transmitted in an SSS may advantageously lead to transmission of SSSinformation in a shorter SSS sequence.

If a PSS carries part of PCI information such as a cell group, thenumber of pieces of PCI information that a UE should acquire from an SSSmay be decreased.

For example, if the UE has acquired two pieces of cell group informationfrom a PSS, the UE may detect a PCI by acquiring information from 252hypotheses from an SSS, along with the information acquired from thePSS. The following specific methods may be considered.

4.5.1 Method 1

The BS may generate an SSS sequence in the form of[g1(n)*c1(n)*s1(n)g2(n)*c2(n)*s2(n)]. Because the scrambling sequences_(k)(n) is PCI-based, a receiver needs 252*2 correlation operations toacquire a PCI and SF position information. Herein, c_(k)(n) (k=1, 2) isa sequence that determines a cyclic shift value in PCI informationacquired from a PSS. c_(k)(n) may be an m-sequence of the same length asg_(k)(n) and s_(k)(n).

4.5.2 Method 2

The BS may generate an SSS sequence in the form of[g1(n)*c1(n)*s1(n)g2(n)*c2(n)*s1(n)]. Because the scrambling sequences_(k)(n) is PCI-based, a receiver needs 252*2 correlation operations toacquire a PCI and SF position information. Herein, c_(k)(n) (k=1, 2) isa sequence that determines a cyclic shift value in PCI informationacquired from a PSS. c_(k)(n) may be an m-sequence of the same length asg_(k)(n) and s_(k)(n).

4.5.3 Method 3

The BS may generate an SSS sequence in the form of[g1(n)*c1(n)g2(n)*c2(n)*s1(n)]. Because the scrambling sequence s_(k)(n)is determined according to a PCI and affects only g₂(n), a UE needs64+252 correlation operations. Herein, c_(k)(n) (k=1, 2) is a sequencethat determines a cyclic shift value in PCI information acquired from aPSS. c_(k)(n) may be an m-sequence of the same length as g_(k)(n) ands_(k)(n).

4.6 Method for Generating SSS without Using Scrambling Sequence

FIG. 20 is a view illustrating a method for generating an SSS withoutconsidering a scrambling sequence.

In FIG. 20, the BS generates K sequences of length Mk. Herein, thelengths of first sequences g_(k)(n) generated by the BS may be equal.The BS generates a sub-sequence to transmit g_(k)(n) in OFDM symbols.Herein, the BS may insert ‘0’ according to the amount of datatransmittable in each OFDM symbol during generation of the sub-sequence.

For example, if the amount of data transmittable in each OFDM symbol isR, the length of a sequence transmittable in N OFDM symbols is N*R,satisfying the relationship that N*R>=K*M_(k). Herein, the number ofOFDM symbols carrying an SSS, N and an information transfer method mayvary according to K and g_(k)(n).

For the convenience of description, it is assumed that SSSs carry 504PCIs and information about the positions of 8 subframes in which SSSsare transmitted. Therefore, the BS preferably designs an SSS sequence sothat a total of 4032 different hypotheses may be distinguished. Inaddition, if M_(k) is different, the sequences have different lengths,and thus correlation performance may be different during reception at aUE.

That is, since the correlation performance is determined by the smallestM_(k) value, it is preferred that the sequences have the same lengthM_(k). As described before in the foregoing embodiments, g_(k)(n) may beapplied to the case where K=2, 3 or K1 (K1 is an integer larger than 3),and for a PCI and SF position information, the value of a column exceptfor columns corresponding to the cyclic shift values of a scramblingsequence, as defined in [Table 11] to [Table 13] may be applied.

5. Apparatuses

Apparatuses illustrated in FIG. 21 are means that can implement themethods described before with reference to FIGS. 1 to 20.

A UE may act as a transmission end on a UL and as a reception end on aDL. An eNB may act as a reception end on a UL and as a transmission endon a DL.

That is, each of the UE and the eNB may include a transmitter (Tx) 2140or 2150 and a receiver (Rx) 2160 or 2170, for controlling transmissionand reception of information, data, and/or messages, and an antenna 2100or 2110 for transmitting and receiving information, data, and/ormessages.

Each of the UE and the eNB may further include a processor 2120 or 2130for implementing the afore-described embodiments of the presentdisclosure and a memory 2180 or 2190 for temporarily or permanentlystoring operations of the processor 2120 or 2130.

The embodiments of the present invention may be performed using thecomponents and functions of the UE and the base station. For example, abase station for transmitting a primary synchronization signal (PSS) ina wireless access system supporting narrowband Internet of things(NB-IoT) may include a transmitter and a processor. The processor may beconfigured to repeatedly generate a first sequence N times in order togenerate the PSS, to multiply the N first sequences by a second sequenceto generate N PSSs, and to control the transmitter to transmit the NPSSs through N orthogonal frequency division multiplexing (OFDM)symbols. At this time, a bandwidth used in the wireless access systemsupporting NB-IoT is one PRB, and the PRB includes 12 subcarriers in thefrequency domain. In addition, the base station may transmit the N OFDMsymbols with “0” filled in resource elements, to which the PSSs are notallocated. The N OFDM symbols may be included in one subframe. The NOFDM symbols may include OFDM symbols except for a control region in thesubframe. The first sequence may be generated from a Zadoff-Chu (ZC)sequence. The second sequence may be determined in consideration of thenumber of OFDM symbols in which the PSS signals are transmitted. Fordetailed descriptions and technical features of the UE, refer to theembodiments described in Chapters 1 to 4.

The Tx and Rx of the UE and the eNB may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDM packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the eNB of FIG. 21may further include a low-power radio frequency (RF)/intermediatefrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a personal communication service (PCS) phone, a globalsystem for mobile (GSM) phone, a wideband code division multiple access(WCDMA) phone, a mobile broadband system (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a multi mode-multi band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory2180 or 2190 and executed by the processor 2120 or 2130. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system.Besides these wireless access systems, the embodiments of the presentdisclosure are applicable to all technical fields in which the wirelessaccess systems find their applications.

What is claimed is:
 1. A method of transmitting a primarysynchronization signal (PSS) in a wireless access system supportingnarrowband Internet of things (NB-IoT), the method comprising: obtaininga Zadoff-Chu (ZC) sequence of length 11 with a root index equal to 5;obtaining a cover code of length 11; and transmitting the PSS through aplurality of orthogonal frequency division multiplexing (OFDM) symbolsbased on applying elements of the cover code to the ZC sequence inrespective OFDM symbols of the plurality of OFDM symbols.
 2. The methodaccording to claim 1, wherein the plurality of OFDM symbols with “0”filled in resource elements, to which the PSS is not allocated, aretransmitted.
 3. The method according to claim 1, wherein the pluralityof OFDM symbols are included in one subframe.
 4. The method according toclaim 3, wherein the plurality of OFDM symbols are OFDM symbols exceptfor a control region in the subframe.
 5. A base station for transmittinga primary synchronization signal (PSS) in a wireless access systemsupporting narrowband Internet of things (NB-IoT), the base stationcomprising: a transmitter; and a processor, wherein the processor isconfigured to: obtain a Zadoff-Chu (ZC) sequence of length 11 with aroot index equal to 5; obtain a cover code of length 11; and control thetransmitter to transmit the PSS through a plurality of orthogonalfrequency division multiplexing (OFDM) symbols based on applyingelements of the cover code to the ZC sequence in respective OFDM symbolsof the plurality of OFDM symbols.
 6. The base station according to claim5, wherein the plurality of OFDM symbols with “0” filled in resourceelements, to which the PSS is not allocated, are transmitted.
 7. Thebase station according to claim 6, wherein the plurality of OFDM symbolsare included in one subframe.
 8. The base station according to claim 7,wherein the plurality of OFDM symbols are OFDM symbols except for acontrol region in the subframe.